The present invention relates to devices for measuring predetermined volumes of a liquid sample and possibly subjecting said volumes to analytical operations.
Previously distributing devices have been developed in which a liquid sample in a storage vessel is distributed among a number of tubes. The distributing device of U.S. Pat. No. 3,770,027 (Guigan) comprises a vertical central tube formed with apertures and connected to a number of test tubes by capillary tubes provided with a constriction. When a liquid storage vessel is slid over to the bottom part of the tube, liquid enters capillary tubes to the constriction therein due to capillary action. When the storage vessel is withdrawn, the portion of liquid sample still in the vertical tube flows down, whereas the portions in the capillary tubes remain inside them. The liquid in each capillary tube can then be spun into a corresponding test tube, simply by rotating the device at a speed sufficient to overcome the capillary forces.
That device is of relatively simple construction. On the other hand, it has drawbacks which are particularly serious when the device is used to distribute samples of infections, noxious or dangerous liquids, e.g. preparations of micro-organisms. The vertical tube remains upwardly and downwardly open after the storage vessel has been removed while it communicates with the filled capillary tubes. The fractions may flow and contaminate the environment if the device is upset or handled carelessly while taken to the centrifuge. The balance of liquid contained in the storage vessel may also be spilled inadvertently. The volume contained in a capillary tube is insufficient for many analytical applications. Due to the small volume of the tubes, it is difficult to construct a device of the afore-mentioned kind wherein the differences in volume between the capillary tubes is negligible as compared with the volume of the tubes.
Another prior art device (U.S. Pat. No. 3,606,083) is similar but includes an annular chamber formed on the upper surface of a disk. Again, there is a substantial risk of spill over. In addition, the liquid which remains available in the annular chamber refills the capillary tubes after the device has been spun to empty the tubes and has come to rest again.
Other known devices for obtaining fractions of samples use centrifugal force to distribute liquid samples from a central well. Devices of this kind are described inter alia in "A miniature fast analyzer system" in Analytical Chemistry, Vol. 45, No. 3, March 1973, pp. 328A-339A.
These device comprise a rotor in which the centrifugal force sprays fractions of a sample from a central well into lateral chambers. Again, that device is not accurate enough for a number of uses.